The present invention relates to a method for manufacturing an optical film, and particularly relates to a method for manufacturing a so-called retardation film using a casting film forming method.
Plastic films have been used as conventional retardation films triacetate films, polyacryl resin films, polycarbonate films, and the like have been employed due to their superior optical transparency and small orientation, due to properties such as their ease of adherence. (See Japanese Patent Unexamined Publication No. Sho. 57-30808). However, conventional films formed using the casting film forming method result in optical anisotropy. Due to these deficiencies, it was necessary in the conventional practice to subject films formed by the above method to a heat treatment so as to reduce the amount of orientation to thereby equalize the retardation.
Additionally, conventional methods have a problem in manufacturing efficiency because an additional step for heat treatment is required for reducing the retardation.